1. Field of the Invention
The present invention relates to a scan type display optical system and a scan type image display apparatus for displaying an image by deflecting and scanning light.
2. Description of Related Art
An optical system in which a screen serving as a face to be projected can be subjected to projection from a slant direction to shorten the distance between the screen and a projector has been proposed as one projection optical system used for projectors. However, projection of an image to the screen from the slant direction induces trapezoidal distortion to the image. Therefore, various proposals for correcting the trapezoidal distortion have been made.
The following Patent Document 1 has proposed a projection optical system in which a lens group is rotated and decentered with a diaphragm as the center by using a coaxial rotational symmetrical f-θ lens to rotate an image surface in a state where there is no trapezoidal distortion of the image.
Furthermore, the following Patent Document 2 has proposed a projection optical system for correcting the trapezoidal distortion at a fixed projection angle by using a decentered aspheric surface.
In an embodiment of an optical system proposed in the following Patent Document 3, a wide-angle lens having a wide field angle is used as a projection optical system, a light valve and a screen are shifted with respect to the optical axis of the projection optical system and projection is carried out by using the end portion of the field angle to thereby construct a slant projection type optical system.
In an embodiment of an optical system proposed in the following Patent Document 4, light is projected slantwise to the screen by inclining first and second projection optical systems with respect to the optical axis.
In a non-axial optical system, Patent Document 5 discloses a designing method and a calculation method of a paraxial amount such as a focusing distance or the like, and Patent Documents 6, 7 and 8 disclose design examples thereof. In these publications, a “reference axis” concept is introduced, and a constituent plane is set to an asymmetric aspheric surface, thereby constructing an optical system for which aberration is sufficiently corrected.
The non-axial optical system as described above is called an Off-Axial optical system. When considering a reference axis along a light ray passing through the center of an image and the center of a pupil, the Off-Axial optical system is defined as an optical system containing a curved surface (Off-Axial curved surface) on which a surface normal at the cross point between the constituent plane and the reference axis is not on the reference axis. In the Off-Axial optical system, the reference axis has a zigzagged shape.
With respect to the Off-Axial optical system, the constituent plane generally becomes non-axial, and no shading occurs even on the reflective surface, so that an optical system using the reflective surface can be easily constructed. Furthermore, by forming an intermediate image in the optical system, an optical system which is compact irrespective of a wide field angle can be designed. The Off-Axial optical system is a front-diaphragm type optical system, but it can be constructed as a compact optical system because the optical path thereof can be relatively freely routed.
By actively using these, Patent Document 9 and Patent Document 10 have proposed a projection optical system for correcting trapezoidal distortion at a fixed projection angle by using a rotational asymmetric reflective surface having curvature.
Furthermore, Patent Document 11 has proposed a technique for secondarily scanning a laser ray with a rotational polygonal mirror to display an image. In this case, by properly setting the timing of intensity modulation of the laser ray, distortion which cannot be removed by the optical system can be corrected.
Patent Document 12 has proposed a projection optical system for carrying out slant projection by using a plurality of reflective surfaces.
Furthermore, an optical device for scanning incident light by deflecting the incident light has been proposed by Patent Documents 13 to 15.
FIG. 28 shows the construction of a planar type galvanomirror proposed in Patent Document 13. Specifically, a planar movable plate 105 and a torsion bar 106 for supporting the movable plate 105 in a movable manner are integrally formed on a silicon substrate 102. A planar coil 107 which is supplied with current to generate magnetic field is equipped at the peripheral edge portion of the upper surface of the movable plate 105, and a reflection mirror 108 is equipped at the center portion on the upper surface surrounded by the planar coil 107. Furthermore, glass substrates 103 and 104 are equipped on the upper and lower surfaces of the silicon substrate 102, and permanent magnets 110A, 110B and 111A and 111B for acting a magnetic field on the planar coil 107 are fixed at predetermined positions of the glass substrates 103 and 104.
[Patent Document 1] Japanese Patent Application Laid-Open No. H9(1997)-304733
[Patent Document 2] Japanese Patent Application Laid-Open No. H10(1998)-282451
[Patent Document 3] Japanese Patent Application Laid-Open No. H5(1993)-100312
[Patent Document 4] Japanese Patent Application Laid-Open No. H5(1993)-80418
[Patent Document 5] Japanese Patent Application Laid-Open No. H9(1997)-5650
[Patent Document 6] Japanese Patent Application Laid-Open No. H8(1996)-292371
[Patent Document 7] Japanese Patent Application Laid-Open No. H8(1996)-292372
[Patent Document 8] Japanese Patent Application Laid-Open No. H9(1997)-222561
[Patent Document 9] Japanese Patent Application Laid-Open No. 2001-255462 (corresponding to U.S. Pat. No. 6,626,541 and EP 1 139 145 A2)
[Patent Document 10] Japanese Patent Application Laid-Open No. 2000-89227
[Patent Document 11] Japanese Patent Application Laid-Open No. H6(1994)-295159
[Patent Document 12] PCT Publication No. WO 97/1787
[Patent Document 13] Japanese Patent Application Laid-Open No. H7(1995)-175005 (corresponding to U.S. Pat. No. 5,606,447 and EP 0 686 863 A1)
[Patent Document 14] Japanese Patent Application Laid-Open No. H7(1995)-218857 (corresponding to PCT Publication No. WO 95/20774, U.S. Pat. No. 5,767,666 and EP 0 062 729 A1)
[Patent Document 15] Japanese Patent Application Laid-Open No. 2000-35549
The Patent Document 1 proposes a projection optical system containing a combination of coaxial rotational symmetric f-θ optical systems is proposed in Patent Document 1, however, it is difficult to apply this projection optical system to a normal projector, etc., because the field angle is narrow.
In the case of normal lenses, as the field angle is increased from the optical axis, the light amount is reduced. Therefore, as a lens system having a wide field angle is more frequently used, the difference in brightness on the image surface is increased more and more. Therefore, the projection optical system proposed by Patent Document 1 is unsuitable for a projector to which a wide field angle and a bright image surface are required.
The projection optical system proposed by Patent Document 2 corrects the trapezoidal distortion by the decentered aspheric surface, however, it can correct the trapezoidal distortion at a fixed projection angle, so that the degree of freedom of the setup position of the projector is lost. Furthermore, from the point of view that the shift amount of the screen is small and it is not telecentric to a liquid crystal panel, this projection optical system is also unsuitable for the projector.
In the projection optical systems proposed in Patent Document 9 and Patent Document 10, the trapezoidal distortion of the wide field angle is corrected by using the rotational asymmetric reflective surface having curvature. However, these systems can correct the trapezoidal distortion only at some fixed projection angle, and the degree of freedom of the setup position of the projector is lost.
In the case of the projection optical system in which the light valve and the screen are shifted with respect to the optical axis as proposed in Patent Document 3, a high field-angle lens system which covers an extremely large field angle is required as a lens system to be used. In addition, when the optical axis is set to approach to the center of the screen, an image is not focused on the screen in the normal lens system, and it is focused on the plane vertical to the optical axis.
When the projection optical system is constructed as described above, as well known, an image is distorted in a trapezoidal shape, and it is out of focus at the upper and lower sides of the screen. When inclination of the image surface is corrected, the correction must be carried out so as to offset the difference between the optical path of a ray passing through the upper portion of the screen and the optical path of a ray passing through the lower portion of the screen. When this optical path difference is corrected, the optical path difference can be reduced if the correction can be carried out in the neighborhood of the image-forming surface, and thus the correction amount can be small. On the other hand, when the correction is carried out on the optical plane at the screen side on which an image is enlarged, the optical path difference has a direct effect.
Furthermore, in the projection optical system proposed in Patent Document 4, the lens system is merely tilted, and thus it is difficult to tilt the image surface sufficiently. Furthermore, when the tilt amount is excessively large, it is difficult to secure the optical performance.
In the optical system proposed in Patent Document 12, the size of one reflective surface is large, and it is difficult to manufacture the optical system with high precision.
In the method of scanning a point light source or a one-dimensional image display element for display by a rotational polygonal mirror, a galvanomirror or the like as disclosed in Patent Document 11 or the like, when electrical correction is impossible, the projection optical system must have the characteristic of a f-θ lens or arcsine lens.
When a one-dimensional image display device is used, it is required to have the characteristic of the f-θ lens, the arcsine lens or the like in the scanning direction and the characteristic of the normal camera lens in the non-scanning direction vertical to the scanning direction. That is, it is required to have a characteristic which is asymmetrical with respect to the optical axis.